Centrifuge construction



Oct. 10, 1950 A. E. ZIMMERMAN ETAL 2,

CENTRIFUGE CONSTRUCTION Filed June 7, 1947 2 Sheets-Sheet 1 FlE L.

INVENTORES A.E.Z/'mmerma'n William/Lfiofie ATTORNEY O 1950 A. E.ZIMMERMAN ETAL 2,525,629

CENTRIFUGE CONSTRUCTION 2 Sheets-Sheet 2 Filed June 7, 194'? mvEN'rorzsA. E. Zimmerman Vl//'///'am A. Sofia:-

ATTORN EY Patented Oct. 10, 1950 CENTRIFUGE CONSTRUCTION Albert E.Zimmerman, Tiburon, and William Arms Botke, Berkeley,

Calif., assignors to Merco Centrifugal 00., San Francisco, Calif., acorporation of California Application June 7, 1947, Serial No. 7 53,302

1 Claim. (Cl. 233-46) This invention relates generally to centrifuges ofthe type adapted particularly for the continuous separation anddischarge of solid components from a feed material containing suspendedsolids.

Continuous centrifuges of the type disclosed in Letters Patent1,923,454, 1,847,751 and 2,060,- 236 utilize a so-called return circuitby means of which a large part of the centrifugally separated underfiowis continuously returned into the centrifuge rotor. A commercial machineof this character makes use of a volute which surrounds the rotor, andwhich receives the centrifugally separated underflow. The rotor isprovided with a lower conical shaped impeller portion which has anaxially disposed opening faced downwardly, and which is adapted toreceive the returned underflow material. A pipe connects from the voluteto a nozzle disposed below the lower end of the rotor, whereby a closedreturn circuit is formed to deliver the underflow into the impellerunder the pressure developed by the volute. The impeller in turn isconstructed in such a manner as to deliver the returned material into anannular chamber forming a part of or communicating with the separatingchamber of the rotor.

With centrifuges as described above a particular problem is involved inconnection with pumping of the returned underfiow material into thecentrifuge separating chamber. For optimum operation the returnedmaterial should be delivered to the separating chamber under arelatively high pressure head consistent with the speed of operation ofthe rotor, and the pressure must be relatively constant to insurestability of operation with a desired maintenance of the gravity of theunderflow. Inability of the impeller or the parts of the return circuitto deliver underflow at a proper pressure head into the separatingchamber serves to limit the speed of operation and the separatingcapacity of the machine. A further difliculty involved is thereintroduction of the underflow into the rotor in such a manner as tominimize spill or material or spraying of the material from the exteriorsurfaces of the rotor. Any spilling or spraying of the material as it isbeing introduced into the rotor, complicates the problem of removingsuch spilled material from the housing of the machine. Also the powerconsumption of the machine is increased, and the dynamic stability ofthe machine is disturbed. In addition such spilled material tends tofind its Way into the collecting means for the separated fractions, thusinterfer ing with the desired sharpness of separation.

It is an object of the present invention to improve upon machines of theabove character, particularly with respect to the means for introducingthe underfiow material back into the centrifuge rotor.

A further object of the invention is to provide an improved centrifugeof the above character which has a new and novel type of pumping orimpeller means for the return of underflow material back into thecentrifuge chamber.

A further object of the invention is to provide improved impeller meansfor a centrifuge of the above type which will minimize any spill orsplashing of material from the rotor.

Additional objects and features of the invention will be apparent fromthe following description in which the preferred embodiment has been setforthin detail in conjunction with the accompanying drawing.

Referring to the drawing Figure 1 is a side elevational view partly insection showing a machine incorporating the present invention.

Figure 2 is an enlarged detail in section illustrating the constructionof the impeller.

Figure 3 is a cross-sectional detail takenalong the line 33 of Figure 2.

Figure 4 is a diagrammatic plan view showing connections for the returnof underflow discharge material to the rotor, for removal of dischargedmaterial, and for introduction of wash liquor.

Figure 5 is a plan detail illustrating the construction of the pick-upring utilized in Figure 3.

The centrifuge illustrated in Figure 1 of the drawing consists generallyof the rotor lln carried by the vertical shaft I I, and disposed withinthe stationary housing l2. As will be presently described the rotor isprovided with various passages, including a passage for the inflow offluid feed material, a passage for discharge of lighter centrifugallyseparated overflow and a passage for supplemental fluid liquid which ispreferably made up of the heavier centrifugally separated dischargematerial or underflow. The rotor shaft II is connected by coupling l3 tothe vertical shaft M of a bearing assembly Iii. The bearin assemblyincludes a ring I! carried, by the spring mounting [9.

The housing l2 can be conveniently formed of a plurality of separablesections l2a, l2b and I20.

Section l2a forms a volute chamber 2| for re-.-

ceiving centrifugally separated overflow, and section l2b is formed toprovide the volute chamber 22 which receives underflow or heavierseparated material.

The body of the rotor i is likewise preferably made of a number ofseparable annular parts, including in this instance the main part lila,and the upper and lower conical shaped parts H12) and H10. Part iiia hasan inner structure 23 which is attached to the lower end of the rotorshaft N. Parts Illa. and [0b are retained together by suitable meanssuch as the expansible clamping ring 24. Within the separating chamber26 of the rotor there is a group of spaced separating discs 21 such asare commonly used in centrifuges. Mounted within the outer peripheralwall 28 of the main body part i iia are the circumierentially spacednozzles 29, each of which is provided with a discharge orifice directedbackwardly with respect to the direction of rotation. The annularperiphery 28 of the rotor body part Hid is accon1- modated within adiverging portion Si or throat ring of the housing part i212.

The lower portion lilo of the rotor forms an impeller for the return ofheavier centrifugally separated underflow material back into the rotor.Thus the lower end of the rotor part We is pro vided with an axially anddownwardly faced opening 44. This opening is directly above a nozble 46carried by the lower part of the housing, and which as will be presentlyexplained serves to direct a jet or solid stream of the returnedunderflow material upwardly into the impeller, and through the openingM. The opening it is formed in a ring 47 which is removably clamped tothe lower part of the body part lilo. The opening 44 is divergentupwardly (Figure 2) and is provided with a plurality ofcircumferentially spaced vanes 38. These vanes have inner verticaledges, and for convenience their outer edges can be fitted withingrooves provided within ring 41 as illustrated. The vanes extend inplanes radial with respect to the axis of rotation.

Ring 47 also serves to mount a vane assembly which extends into theimpeller, and which aids in securing the desired pumping action with aminimum of spill. This assembly consists of a plurality ofcircumferentially spaced and vertically extending vanes which have theirlower ends attached to the ring iii, and their upper ends attached tothe disc The vanes 49 are inclined to the direction of rotation asindicated in Figure 3, and preferably they are slightly curved wherebytheir convex faces are toward the direction of rotation. In general itcan be explained at this point that when a jet of the return underflowmaterial is discharged upwardly from the nozzle 36 into the lowerportion of the rotor, it is spread laterally by impact with the disc 5i,and then acted upon by the rotating vanes 49 to force the materialoutwardly in a radial direction without material splatter.

Surrounding the vanes 59 are the radially tending vertical webs or vanes52 which serve to act upon and impart rotary velocity to the material.The material passing through the spaces between the vanes 52 passesupwardly through passages 53 to the outer annular space 5 which forms apart of or communicates with the main separating chamber 26, and whichalso communicates with the discharge nozzles 29. The inner walls ofpassages 53 are defined by the conical-shaped member 56, which isupwardly divergent, and which is attached to the struc ture 23.

It is desirable to incorporate with the machine means such as disclosedand claimed in co-pending application Serial No. 753,301, filed June '7,1947, which serves to collect and return material which is spilled intothe housing l2. Thus the lower portion I20 of the housing is conicalshaped, whereby spilled fluid material is collected in the lower part ofthe housing and in the proximity of the lower end of the rotor. Thelower end wall 6! of the housing is fitted with the nozzle 46, and itwill be noted that the mounting of the parts is such that an annularspace is provided between these parts and the adjacent lowermost end ofthe rotor. Interposed within this space there is a relatively fiat ring62 which is mounted in spaced relationship with the lower wall of thehousing, as by means of spacing studs 63. The inner edge portion 64 ofthis ring is bent upwardly as illustrated in Figure 2, and the opening66 within the ring is slightly larger than the opening in the nozzle 46and slightly smaller than the opening 4 3. The outer edge portion of thering can be bent upwardly as illustrated and formed in a mannerdisclosed in said co-pending application to provide a plurality ofcircumferentially spaced defleeting vanes 67 which aid in directingcollected spilled material into the space 68 underlying the ring 62. Itwill be evident that when a jet of material is discharging upwardlythrough the nozzle 48 the proximity of the inner edge of ring 62 to thejet of material causes an aspirating action which sucks material throughthe space 88. Thus when spilled material drains to the lower portion ofthe housing it is immediately sucked through the space 68 to merge withthe jet of returned material.

As illustrated diagrammatically in Figure 4' the material collected involute 22 discharges through the tangential pipe 69, and pipe 10,

whereby the underflow material is delivered to the space 7| directlybelow the opening of the nozzle 46. A valve controlled pipe '22 is alsoprovided for the removal of underflow material from the system, and anadditional pipe '13 connects with the pipe 16 to enable introduction ofa supplemental wash liquid, such as fresh water. Considerable fluidpressure is developed by the volute 22 whereby the underfiow materialdischarges upwardly through the opening 44 with considerable velocityand in the form of a relatively compact upwardly directed jet.

In place of a return circuit as described above, we may use a circuitincluding a vent box as disclosed in Peltzer 2,039,605.

Operation of the centrifuge described above is as follows: Assuming thatthe machine is being rotated at a suitable speed and is being suppliedwith a feed material containing solid constituents, a heavier underfiowis established from the peripheral nozzles 29 and is received in thevolute 22. The centrifugally separated overflow is continuouslydischarged over lip 43 and received in chamber 2!. Pressure developed inthe volute 22 causes flow under pressure through the pipes 69 and 78whereby underfiow material is discharged back into the rotor through thenozzle it, in the form of a, compact upwardly directed jet as previouslydescribed. This jet strikes the disc 5! and is deflected or spreadradially, whereby the material is immediately acted upon by the inclinedvanes 59. These vanes serve to force the material outwardly into thezone of operation of the vanes 52 without however imparting any greatamount of rotary velocity to the same, and without such impact as mightcause splashing or splattering. Vanes 52 immediately act upon the fluidmaterial to impart rotary velocity to the same, and the material passesbetween these vanes to passages 53 and from thence into the space 54.The pumping action just described supplies the material to the space 53under considerable pressure, whereby proper separating conditions can beobtained within the centrifuge chamber at relatively high speeds andwithin the centrifuge chamber at relatively high speeds and capacity.

Any spray or splash-back which may tend to occur from within theimpeller is largely trapped by the vanes 48 and delivered back into theim peller. Also the overlapping relation of the inclined vanes 49 tendsto minimize and prevent any splash-back from the spaces between thevanes 52.

We claim:

In a continuous centrifuge of the type including a vertically disposedrotor arranged for separate discharge of centrifugally separatedunderflow and overflow fractions, and having means for separatelycollecting the underflow and overflow fractions and for continuouslyreturning a substantial part of the underfiow material back into thecentrifuge rotor, an impeller forming the lower part of the rotor, anozzle ring attached to the lower end of the impeller and providing alower axial opening faced downwardly, said opening being proportioned toreceive an upwardly directed jet of returned underflow material, a vaneassembly within the impeller of 6 I the rotor and disposed above saidopening, said assembly comprising a plurality of circumferentiallyspaced and vertically extending vanes mounted upon and extendingupwardly from the ring, said vanes being inclined to the direction ofrotation, and a plurality of vanes mounted within the impeller andsurrounding said first named vane assembly, said last vanes serving toimpart rotary velocity to the returned material after such materialpasses between the first vanes whereby the returned material isdelivered under pressure to the separating chamber of the rotor, saidfirst named vanes forming means serving to seal against back splash fromthe vanes of the impeller.

ALBERT E. ZIMMERMAN. WILLIAM ARMS BOTKE.

REFERENCES CI TED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

